I feel a bit sorry for Gilberto as things haven't really gone well for him this season through no fault of his own. The warning sign for me was when despite being vice-captain last season (with the captain being sold), he was overlooked for the captaincy and was effectively demoted - not even vice captain any more.
He was then 'rested' after the Copa America which allowed the lines of Flamini to muscle his way in. Part of me wonders if that was just Wenger trying to protect his ego initially as he sought to freshen the team up a bit - in the same way he kept saying Lehmann was 'injured' long after he was back in training and the Germany squad.
Either way I still reckon Gilberto has a lot to offer the club in terms of his experience, physical presence and also the ability to slot in as an emergency centrehalf shouls Glass get himself injured again.
The one deciding factor of course could be the player himself, at his age he probably wants to be playing every week and the club may decide to cash in.